Christopher dorner posted a manifesto online as the killings began. 11,000 words. And investigators are combing for clues right now. Our senior justice correspondent, pierre thomas, is in los angeles... See More
Christopher dorner posted a manifesto online as the killings began. 11,000 words. And investigators are combing for clues right now. Our senior justice correspondent, pierre thomas, is in los angeles with the latest on that. Good morning, pierre. Reporter: Good morning, george. Authorities say christopher dorner is their worst nightmare. A one-time police officer with military training gone bad. In short, lethal. Dorner, a former navy reservist, is an expert marksman. Authorities are especially worried because he claims to have explosives and a .50 caliber rifle, capable of slicing through armored car from a long distance. In this case, you have a trained officer, a trained member of the military, that's taking that experience and terrorizing this entire region. Reporter: By all accounts until recently, the 33-year-old led a normal life. Always smiling. Very positive. Very upbeat. The kind of person you would want as a friend. Reporter: Dorner appears to have joined the military and later the police out of a sense of honor. In many photographs, he's seen in uniform with a warm smile. But police say behind it is a burning hatred for the lapd, which he calls corrupt and rayist. His battle began in 2006, after he became a p, when he witnessed a fale officer using excessive force. Sources believe he recently snapped after exhausting all avenues to get his good name back. He wanted to be part of something that he believed in. He said, you're always on duty when you're a cop. Reporter: Arianna williams is his former girlfriend. She now fears for her life. I have my phone on 911 when i open the door to my apartment. This will probably end badly for him. I don't see a peaceful resolve or ending in this because he's created so many heinous acts at this point. Reporter: Dorner says he plans to use every bit of his training to kill police, which he calls high-value targets. He says he's prepared to die. And, george, my sources say, believe him. Pierre, thanks very much.
This transcript has been automatically generated and may not be 100% accurate.